Method and apparatus for producing a tubular container while maintaining a shoulder section thereof at a desired thickness, and method for producing a marbleized pattern on a multi-layer tubular container

ABSTRACT

PCT No. PCT/JP96/03833 Sec. 371 Date Aug. 26, 1997 Sec. 102(e) Date Aug. 26, 1997 PCT Filed Dec. 26, 1996 PCT Pub. No. WO97/24219 PCT Pub. Date Jul. 10, 1997A method of producing a tubular container which can efficiently and integrally produce a thinly walled neck section on the tubular container without altering the appearance and profile of the container. The method of producing a tubular container comprises the first step of arranging a thinly walled tube to a tube holder, the second step of softening the inside of the front end of the thinly walled tube, the third step of shrinking the front end of the thinly walled tube, and the fourth step of forming a neck section and a shoulder section to the front end of the thinly walled tube by means of a male mold. After heating the thinly walled tube with hot air, the air is drawn and removed, and the outer wall surface is cooled so as to make the subsequent steps to be conducted smoothly and efficiently. Since hot air is drawn after heating the outer wall surface, a thinly walled tapered shoulder section can be produced without altering the appearance and profile of the tubular container. Also a marble pattern can be formed on the neck section and the shoulder section at the time of molding the tubular container.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of producing a tubular containerintegrally with a neck section from a thinly walled tube ofthermoplastic resin. It also relates to an apparatus for producing sucha container.

2. Background of the Invention

A method of producing a tubular container having a neck section from aparison by blow molding is known. However, the known method has adrawback that the shoulder section of the molded container shows a thickshoulder section because this section is stretched with a low stretchratio. The wall thickness of the parison has to be finely regulated toovercome this drawback but the operation of such fine regulation isdifficult. If the wall thickness of the parison is finely regulated,there arises an additional problem of the difficulty with which a blownozzle can be introduced into the parison through the neck section whenthe neck section has a small diameter. Still additionally, there is alsoa problem that the parting line of the mold halves are transferred tothe surface of the blow molded container when the mold is opened. Whenthe parting line is transferred to the surface of the tubular container,it is hardly adapted to printing.

A known method of producing a tubular container proposed to overcome theabove identified drawbacks comprises steps introducing a heater into athinly walled tube and causing hot air to hit the inner wall surface ofthe thinly walled tube and soften the front end of the thinly walledtube, thereafter discharging hot air through the front end of the thinlywalled and heated tube to the outside to make the front end show aconical profile and then forming a neck section by applying acompression molding means from the inside of the thinly walled tube.

However, with this known method, the thinly walled and heated tube isoutwardly expanded to deform its appearance when hot air is dischargedfrom the inside of the tube because no measures are taken to preventsuch deformation of the thinly walled tube and hot air is made to flowtoward the inner wall surface of the tube and away from the neck formingsection.

With this known technique, therefore, the producing efficiency isreduced particularly when the thinly walled tube is externally heattreated to gather resin to the front end of the thinly walled tube inorder to produce a neck section there because the front end of thethinly walled tube can be introduced into an external heater only withdifficulty. Additionally, unnecessary portions of the thinly walled tubecan be heated and deformed because the area of the outer wall surface ofthe thinly walled tube to which hot air is discharged is not accuratelydefined. The net result will be a tubular container having adisproportionately thick shoulder section due to the large volume ofsoftened resin gathered to produce the neck section or a deformedcontainer having poor commercial value. Another problem is that the necksection cannot be produced after the surface of the tubular container issubjected to a printing process if the thinly walled tube has beendeformed.

SUMMARY OF THE INVENTION

In view of the above identified problems of the prior art, it istherefore an object of the present invention to provide a method ofproducing a tubular container to show a desired tubular profile with anenhanced efficiency. Another object of the invention is to provide anapparatus for producing such a tubular container.

When decorating the shoulder section of a tubular container with amarble pattern according to a prior art process, the marble pattern istypically formed on the shoulder section by printing after producing thetubular container. According to the invention, to the contrary, a marblepattern can be formed on the shoulder section of the tubular containerduring the manufacture of the container.

(1) According to the invention, a method of producing a tubularcontainer having a neck section for receiving a cap from a thinly walledtube of thermoplastic resin comprises the four steps as follows.

In the first step, the thinly walled tube is arranged on a tube holderwhich has a head forming section for forming the neck section. A frontend of the thinly walled tube is arranged to project by a given distancefrom the front end of the tube holder.

In the second step, an inside of the front end of the thinly walled tubeis softened while maintaining the profile of the front end of the thinlywalled tube by establishing a temperature difference between the insideand the outside of the thinly walled tube. Hot air is discharged ontothe inner wall surface of the front end of the thinly walled tube. Thedischarged air is forcibly drawn in the direction moving away from amale mold. At the same time the outer wall surface of the front end ofthe thinly walled tube is cooled.

In the third step, the front end of the thinly walled tube is shrunk bydischarging hot air onto the outer wall surface of the front end of thethinly walled tube and forcibly drawing the hot air in the directionmoving away from the male mold.

In the fourth step, a neck section and a shoulder section are formedfrom the front end of the shrunk thinly walled tube by means of a femalemold and the male mold.

Because the hot air used to heat the inner wall surface of the thinlywalled tube is forcibly drawn and removed, no undesired area of theinner wall surface is heated. Also, because the outer wall surface ofthe thinly walled tube is cooled simultaneously and any possibledeformation due to expansion is prevented, the profile of the thinlywalled tube can be kept unchanged before and after the heating.Additionally, since the hot air used to heat the outer wall surface ofthe thinly walled tube is forcibly drawn and removed, no undesired areaof the outer wall surface is heated. Thus, the volume of the portion tobe softened to produce the neck section can be held to a given level andthe shoulder section can be made to have a desired thickness so thatconsequently a tubular container having a desired profile can beobtained.

(2) An outlet for pouring out the content may be produced in the necksection at the time when the neck section and the shoulder section areformed by compression molding or a closed neck section may be formed bycompression molding and an outlet may be formed after molding the necksection.

(3) The thinly walled tube may be a multilayer tube or a monolayer tube.

(4) The thinly walled tube may be a three-layer tube having anintermediary layer sandwiched by an outer layer and an inner layer andthe intermediary layer may be made of a material different from those ofthe outer and inner layers, the inner layer having a thickness greaterthan the outer layer.

By making the inner layer thicker than the outer layer, the productionof defectively molded tubular containers can be prevented when the necksection is formed by compression molding.

(5) The thinly walled tube may be a three-layer tube having anintermediary layer sandwiched by an outer layer and an inner layer andthe intermediary layer may be made of a material different from those ofthe outer and inner layers, the material of the inner layer having afluidity greater than the material of the outer layer.

By making the material of the inner layer show a fluidity different fromthe material of the outer layer, the former having fluidity greater thanthe latter, any unevenness in the linearity of the junction of thedifferent resin materials can be prevented from occurring.

(6) The thinly walled tube may be a three-layer tube having anintermediary layer sandwiched by an outer layer and an inner layer andthe intermediary layer may be made of a material different from those ofthe outer and inner layers, the inner layer having a thickness greaterthan the outer layer, the material of the inner layer having a fluiditygreater than the material of said outer layer.

By making the inner layer thicker than the outer layer, the productionof defectively molded tubular containers can be prevented when the necksection is formed by compression molding. By making the material of theinner layer show a fluidity different from the material of the outerlayer, the former having fluidity greater than the latter, anyunevenness in the linearity of the junction of the different resinmaterials can be prevented from occurring.

(7) According to the invention, an apparatus for producing a tubularcontainer having a neck section for receiving a cap from a thinly walledtube of thermoplastic resin comprises a tube holder, an internal heater,an external heater and a female mold.

The tube holder holds a thinly walled tube, and includes a male mold forcompression molding. The male mold is inserted into the thinly walledtube. The male mold is arranged inwardly in an axial direction from thefront end of the thinly walled tube by a given distance. The tube holderis axially movable.

The internal heater discharges hot air onto the inner wall surface ofthe front end of said thinly walled tube. Also, the internal heatercools the outer wall surface of the front end of the thinly walled tube.The internal heater also draws the hot air axially in the directionmoving away from the thinly walled tube after the inner wall is heated.

The external heater discharges hot air onto the outer wall surface ofthe front end of said thinly walled tube. Also, the external heaterdraws the hot air axially in the direction moving away from the thinlywalled tube after the outer wall surface is heated.

The female mold cooperates with the male mold of said tube holder topinch the front end of the thinly walled tube and form the neck sectionand the shoulder section by compression molding.

The above described producing method can be practiced easily by using anapparatus for producing a tubular container according to the invention.

(8) An apparatus for producing a tubular container according to theinvention may be provided with a piercing device for forming an outletthrough the neck section when producing a neck section and a shouldersection by means of the male mold and the female mold of the tubeholder.

(9) The internal heater of an apparatus for producing a tubularcontainer according to the invention may comprise an annular coolingsection for cooling the outer wall surface of the front end of thethinly walled tube, a heating section arranged inside the coolingsection with an annular gap provided between itself and the coolingsection and a hot air suction path communicating with the annular gap sothat the front end of the thinly walled tube held by the tube holder canbe inserted into the annular gap between the cooling section and theheating section, the heating section being provided in the inside with ahot air path and a hot air discharge port at a position facing thecooling section with the thinly walled tube disposed therebetween.

(10) The external heater of an apparatus for producing a tubularcontainer according to the invention may comprise an annular heatingsection provided in the inside with a hot air path so that the front endof the thinly walled tube held by the tube holder can be inserted intothe inside of the heating section, a suction path being connected to theinside of the heating said heating section, the heating section beingprovided with a hot air discharge port on the inner wall surface facingthe front end of the inserted thinly walled tube.

(11) A thinly walled tube to be used for the purpose of the inventionmay be, not limitatively, made of adhesive polyethylene and resin havinggas barrier properties such as ethylene vinylalcohol copolymer.

(12) According to the invention, a method of producing a tubularcontainer having a neck section for receiving a cap from a thinly walledmultilayer tube made of thermoplastic resin and having a elliptic crosssection and forming a marble pattern on the tubular container comprises:

the first step of putting the thinly walled tube on a tube holder havinga neck forming section for forming the neck section and causing thefront end of the thinly walled tube to project by a given distance fromthe front end of the tube holder;

the second step of softening the inside of the front end of the thinlywalled tube, maintaining the profile of the front end of the thinlywalled tube, by discharging hot air onto the inner wall surface of thefront end of the thinly walled tube and forcibly drawing the dischargedair in the direction moving away from said male mold, while cooling theouter wall surface of the front end of the thinly walled tube toestablish a temperature difference between the inside and the outside ofthe thinly walled tube;

the third step of shrinking the front end of the thinly walled tube toadhere by discharging hot air onto the outer wall surface of the frontend of the thinly walled tube in the direction moving away from the malemold; and

the fourth step of forming a neck section and a shoulder section fromthe front end of the shrunk and adhered thinly walled tube by means of afemale mold cooperating with the male mold.

The layers of the multilayer tube are preferably and respectivelycolored with desired colors.

With a method of producing a marble pattern on a tubular containeraccording to the invention as described above, the front end of thethinly walled tube is shrunk and folded to the inside in the third step.Since the neck section and the tube holder are formed from the front endby compression molding under this condition in the fourth step, thefolded portion shows phase difference, overlapping and displacementbetween the inner and outer layers to consequently stretch the outerlayer and make it thin. In the area where the outer layer is made thin,the intermediary later and the inner layer can be seen through the outerlayer to produce a marble pattern along the generatrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a thinly walled tube that can be used for afirst embodiment of the invention.

FIG. 2 is a front view of the tube holder used in the first step of thefirst embodiment of the invention.

FIG. 3 is a cross sectional view of the tube holder of the firstembodiment of the invention and the thinly walled tube held by the tubeholder.

FIG. 4 is a cross sectional view of the internal heater of the firstembodiment of the invention.

FIG. 5 is a cross sectional view of the tube holder and the thinlywalled tube held by the tube holder after the heat treatment of thesecond step of the first embodiment of the invention.

FIG. 6 is a cross sectional view of the external heater of the firstembodiment of the invention.

FIG. 7 is a front view of the tube holder and the thinly walled tubeheld by the tube holder immediately after the heat treatment of thethird step of the first embodiment of the invention.

FIG. 8 is a front view of the tube holder and the thinly walled tubeheld by the tube holder after the heat treatment of the third step ofthe first embodiment of the invention.

FIG. 9 is a cross sectional view of the male mold before molding theneck section in the fourth step of the first embodiment of theinvention.

FIG. 10 is a cross sectional view of the male mold when molding the necksection in the fourth step of the first embodiment of the invention.

FIG. 11 is a cross sectional view of the male mold after molding theneck section in the fourth step of the first embodiment of theinvention.

FIG. 12 is a cross sectional view of a tubular container produced by thefirst embodiment of the invention.

FIG. 13 is a longitudinal cross sectional view of a thinly walled tubethat can be used for the first or second embodiment of the invention.

FIG. 14 is a cross sectional view of a tubular container produced by thethird embodiment of the invention.

FIG. 15 is a partial front view of the shoulder section and the necksection of a tubular container produced by the third embodiment of theinvention.

FIG. 16 is a cross sectional partial view take along line A--A of FIG.17.

FIG. 17 is a partial front view of the thinly walled tube held by thetube holder after the heat treatment of the third step of the thirdembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Now, the present invention will be described by referring to FIGS. 1through 13 illustrating the first embodiment of the invention.

Firstly, a tubular container manufactured by the method of the inventionwill be described by referring to FIG. 12. A tubular container 1includes a barrel section 3 and neck section 5. The barrel section isformed by thermal molding a cylindrical, soft and thinly walled tuberesin. The neck section is formed by compression molding the resin. Thebarrel section 3 comprises a straight barrel section 7 and a taperedshoulder section 9. The neck section 5 has an outlet 11 at an endthereof for pouring a content (not shown) therethrough and is providedwith a screw thread 13 on an outer wall surface for engagedly receivinga cap.

The tubular container 1 is formed by one-piece molding thinly walledtube 15. As shown in FIG. 1, the thinly walled tube 15 is a cylindricalpiece with a given length, and formed by heating adhesive polyethyleneand a resin having gas barrier properties such as ethylene vinylalcoholcopolymer, stretching the heated material, extrusion molding it, andcutting in the given length.

The thinly walled tube 15 may be a monolayer tube or a multilayer tube.For example, as shown in FIG. 13, the thinly walled tube 15 may have athree-layer structure comprising an outer layer 61, an inner layer 63and an intermediary layer 65 sandwiched by the outer and inner layers.However, the present invention is not limited to the three-layerstructure.

The outer layer 61 may be made of any known resin material adapted toproducing tubular containers. Materials that can be used for the outerlayer include polyethylene (PE) and polypropylene (PP) which have aprintability, but the present invention is not limited to thesematerial.

The inner layer 63 and the intermediary layer 65 may be made of anyknown resin material having desired physical and chemical properties. Ifgas barrier properties is expected, either the inner layer 63 or theintermediary layer 65 may be made of a resin material having gas barrierproperties. Resin materials having gas barrier properties includeethylene vinylalcohol copolymer (EVOH), polyethylene terephthalate(PET), PET-G (a polyethylene terephthalate type thermoplasticcopolyester where glycol is partly substituted by 1,4-cyclohexanediinethanol) and polybutylene terephthalate (PBT). If the container isto be filled with liquid containing vitamin or a coloring agent, theinner layer 63 may suitably be made of an unadsorptive resin material. Atypical unadsorptive resin material is unadsorptive PET.

Each of the outer layer 61, the inner layer 63 and the intermediarylayer 65 may be made of an adhesive resin material to eliminate the useof adhesive agent. Adhesive resin materials include adhesivepolyethylene such as ADMER (tradename: available from MitsuiPetrochemical Industries) and MODIC (tradename: available fromMitsubishi Chemical Industries), although other materials may also beused. If adhesive resin is not used, known adhesive agents may be used.

Thus, the present invention includes not only a tubular container havinga two-layer structure of adhesive polyethylene and EVOH, but also atubular container having a three-layer structure of non-adhesivepolyethylene, adhesive agent and EVOH. Also, the present inventionincludes a tubular container having a five-layer structure ofpolyethylene, adhesive agent, EVOH, adhesive agent and polyethylene.

The thinly walled tube 15 may show a circular or elliptic crosssectional view.

Now, a first embodiment of apparatus for producing a tubular containerby means of the method of the present invention will be described byreferring to FIGS. 2, 4. 6 and 9.

The producing apparatus comprises a tube holder 17, an internal heater23, an external heater 25, a female mold 27 and a piercing device 29.

The tube holder 17 is used to hold the thinly walled tube 15 and to formthe neck section 5 and the tapered shoulder section 9 by compressionmolding. The tube holder includes a tube holder main body 31 and a malemold 16. The male mold 16 and the tube holder main body 31 shows acircular cross sectional view as the thinly walled tube 15. The malemold 16 is arranged at the front end of the tube holder main body 31 andmovably relating to the holder main body 31. As shown in FIG. 3, thethinly walled tube 15 is held by the tube holder main body 31 of thetube holder 17 with its front end projecting from the front end of thetube holder 17 by a predetermined length.

The internal heater 23 is used to heat an inner wall surface 19 of thethinly walled tube 15 and to cool an outer wall surface 21 of the thinlywalled tube, so as to soften the inner wall surface 19 while producing atemperature difference between the inside and the outside of the thinlywalled tube 15. As shown in FIG. 4, the internal heater 23 has anannular cooling section 33 for cooling the outer wall surface 21 of thefront end 15a of the thinly walled tube 15, a heating section 37arranged inside the cooling section 33 with an annular gap 35 providedtherbetween and a hot air suction path 39 communicating with the annulargap 35.

The cooling section 33 includes a circulating section 41 for constantlycirculating a coolant such as water therethrough and a cooling surface43 for cooling the outer wall surface 21 of the thinly walled tube 15 sothat the outer wall surface 21 of the thinly walled tube 15 is cooled asthe cooling surface 43 is held in contact with the outer wall surface 21of the thinly walled tube 15.

The heating section 37 is realized in the form of a hollow cylindercommunicating with a heat generator (not shown) and closed at the top.The heating section 37 has a small diameter section 37a at an upperportion thereof so that it may be inserted into the front end 15a of thethinly walled tube 15. The lower portion of the heating section 37 is alarge diameter section 37b that communicates with the small diametersection 37a. At an upper portion of the small diameter section 37a,there is provided a hot air discharge port 45 facing to the coolingsection 33. The thinly walled tube 15 can be disposed between the hotair discharge port and the cooling section.

The hot air suction path 39 communicating with the gap 35 is alsocommunicating with a hot air suction means (not shown) to draw hot airaway from the front end 15a of the thinly walled tube 15.

The external heater 25 is designed to heat the outer wall surface 21 ofthe front end 15a of the thinly walled tube 15. As shown in FIG. 6, theexternal heater has an annular heating section 49 which contains a hotair flow path 47. The front end 15a of the thinly walled tube 15 held bythe tube holder 17 can be inserted into the heating section 49. Aninside of the heating section 49 communicates with a hot air suctionpath 51. A hot air discharge port 53 is arranged in the heating sectionat a position where the inserted front end 15a of the thinly walled tube15 faces to.

As shown in FIG. 9, the female mold 27 includes a first metal mold 55and a second metal mold 57. The first metal mold 55 has a cavity 55awith a profile corresponding to the external contour of the taperedshoulder section 9 of the tubular container 1. The second metal mold isarranged under the first metal mold 55 and has a cavity 57a with aprofile corresponding to the external contour of the neck section 5. Thepiercing device 29 for forming the outlet 11 in the neck section 5 isarranged below the second metal mold 57. The piercing device 29 is urgedupwardly in FIG. 9 by a resilient means such as a spring. When the frontend 15b of the thinly walled tube 15 is compression molded by the malemold 16 and the female mold 27, the piercing device forms the outlet 11in the neck section 5.

Now, the method of producing a tubular container according to theinvention will be described by referring to FIGS. 1 through 11.

FIGS. 1 through 3 illustrate the first step of arranging a piece ofmaterial resin for the tubular container 1 in position.

As shown in FIG. 3, the thinly walled tube 15 for producing a tubularcontainer 1 is arranged around the tube holder 17. The front end of thethinly walled tube projects axially and outwardly from the front end ofthe male mold 16 by a given distance. Even if the thinly walled tube 15is arranged around the tube holder 17, the male mold 16 can be axiallymoved within the tube holder 17.

FIGS. 4 and 5 illustrate the second step of softening the inner wallsurface 19 of the thinly walled tube 15.

The tube holder 17 carrying the thinly walled tube 15 on the outerperipheral surface thereof is moved until the front end 15a of thethinly walled tube 15 is introduced into the gap 35 between the coolingsurface 43 of the internal heater 23 and the small diameter section 37aof the heating section 37. Then, the inner wall surface 19 of the thinlywalled tube 15 is heated by the heating section 37 while the outer wallsurface 21 is cooled by the cooling surface 43. The heating is conductedby flowing hot air in the heating section 37 and discharging it throughthe hot air discharge port 45 along the direction indicated by thearrows in FIG. 4, so as to soften the inner wall surface 19. The hot airapplied to the inner wall surface 19 is forcibly drawn downwardly inFIG. 4 through the hot air suction path 39 by a suction means (notshown). Thus, the areas of the thinly walled tube 15 that should not beheated is minimally affected by the heating.

The hot air temperature and the duration of time of the heating are soselected as to sufficiently soften the inner wall surface 19 of thethinly walled tube 15. While specific values are cited for the hot airtemperature in the examples described hereinafter, it is not limited tothose values by any means. The duration of time of the heating is alsonot limited to the examples. It should be noted, however, that the resinmaterial of the thinly walled tube would become molten if the hot airtemperate is too high. Therefore, it is preferable to control theheating by controlling the duration of time.

The cooling is conducted by constantly circulating a coolant such aswater in the circulating section 41 to absorb heat from the outer wallsurface 21 of the thinly walled tube 15 that is held in contact with thecooling surface 43. Because the outer wall surface 21 of the thinlywalled tube 15 is cooled, the outer wall surface 21 is prevented frombecoming soft, so as to maintain the profile of the front end 15a of thethinly walled tube 15.

As the inner wall surface 19 of the thinly walled tube 15 is softened,the front end 15a of the thinly walled tube 15 comes to show anincreased wall thickness and a reduced length as shown in FIG. 5. Thismay be because the front end 15a of the thinly walled tube 15 producedby stretch and extrusion molding is heated at temperature above theglass transition temperature of the thinly walled tube 15 by the heatingsection 37 so that it contracts and recovers the original profile due tothe memory. The contracted front end 15a of the thinly walled tube 15provides a certain volume of resin required for forming the neck section5 and the tapered shoulder section 9.

FIGS. 6 through 8 illustrate the third step of softening the outer wallsurface 21 of the front end 15a of the thinly walled tube 15.

The tube holder 17 carrying the thinly walled tube 15 whose front end15a has been made to show a large wall thickness then moved until thefront end 15a of the thinly walled tube 15 is inserted into the heatingsection 49 of the external heater as illustrated in FIG. B. Then, theouter wall surface 21 of the thinly walled tube 15 is heated by means ofa heater 49 positioned around the outer peripheral surface of the frontend 15a of the thinly walled tube 15. The outer wall surface 21 of thethinly walled tube 15 is exposed to hot air discharged from the hot airdischarge port 53 to consequently heat the outer wall surface 21 of thethinly walled tube 15. After contacting with the outer wall surface 21,the hot air is drawn and removed along the hot air suction path 51 asillustrated in FIG. 6 in order to make the front end 15a of the thinlywalled tube 15 to deform or shrink inwardly and, at the same time, tominimize the influence of hot air to the areas that should not beaffected by heat.

The hot air temperature and the duration of time of the heating are soselected as to sufficiently soften the front end 15a of the thinlywalled tube 15. While specific values are cited for the hot airtemperature in the examples described hereinafter, it is not limited tothose values by any means. The duration of time of the heating is alsonot limited to the examples. It should be noted, however, that if thehot air temperature is too high, the resin material of the thinly walledtube would become molten, and, therefore, it is preferable to controlthe heating by controlling the duration of time.

As the outer wall surface 21 is heated, the front end 15b of the thinlywalled tube 15 is deformed toward the inside of the thinly walled tube15 as shown in FIG. 7 and then thermally contracts as shown in FIG. 8.The contracted or shrunk portion of the thinly walled tube 15 provides acertain volume of resin required for forming the neck section 5 and thetapered shoulder section 9.

The extent of external heating depends on the volume required forforming the neck section 5 and the tapered shoulder section 9. Forexample, if the thinly walled tube 15 has a diameter of 19 mm, thethinly walled tube 15 is heated by a length of 15 mm from the front end,and if the thinly walled tube 15 has a diameter of 22 mm, it is heatedby a length of 22 mm from the front end, although the present inventionis not limited to these values.

FIGS. 9 through 11 illustrate the fourth step of forming the necksection 5 and a tapered shoulder section 9 for the tubular container 1.

The tube holder 17 holding the thinly walled tube 15 whose front end 15bhas been contracted is then moved above the female mold 27 as shown inFIGS. 9 and 10. Then, the tube holder 17 is moved downwardly until thefront end 15b is placed on the female mold 27. Subsequently, the malemold 16 is moved downwardly relative to the tube holder 17. The malemold 16 and the female mold 27 hold the front end 15b of the thinlywalled tube 15 therebetween and form the neck section 5 and the taperedshoulder section 9 by compression molding. At the same time, the outlet11 is formed in the neck section 5 by means of the piercing device 29 asshown in FIG. 10.

After the compression molding process is over, the tube holder 17holding the thinly walled tube 15 is moved upward and then the thinlywalled tube 15 is removed from the tube holder 17 to complete theoperation of producing the tubular container 1 as shown in FIG. 12.

EXAMPLE 1

The thinly walled tube 15 was prepared from adhesive polyethylene andEVOH copolymer having gas barrier properties. The wall thickness of thethinly walled tube was 0.5 mm. The outer layer and the inner layer weremade of the adhesive polyethylene, whereas the intermediary layer wasmade of EVOH. The thinly walled tube 15 had a diameter of 19 mm.

The internal heater 23 was used to operate in a manner as describedbelow. Air was heated by it to 380° C., and the air pressure was 0.08MPa (the air flow rate was 410 N1/min). The suction force of heated airwas 330 N1/min. The heating time was 1 second.

The external heater 25 was used to operate as follows. Air was heated byit to 300° C., and the air pressure was 0.09 MPa (the air flow rate was380 N1/min). The suction force of heated air was 350 N1/min. The waterflow rate of the cooling section was 2.2 1/min. The heating time was 4seconds. The thinly walled tube 15 was heated by 15 mm from the frontend of the tube.

As a result, a good tubular container 1 was produced.

EXAMPLE 2 through 5

In these examples, the thinly walled tubes 15 as listed in Table 1 wereused to produce respective tubular containers 1. Table 1 shows how theinternal heater 23 and the external heater 25 were used for eachexample.

As a result, a good tubular container 1 was produced in each example.

                                      TABLE 1                                     __________________________________________________________________________               Example 2  Example 3  Example 4  Example 5                         __________________________________________________________________________    thinly walled tube                                                                     15                                                                     outer layer  adhesive polyethylene low density polyethylene low density                                                 polyethylene low density                                                      polyethylene                        inner layer  EVOH adhesive polyethylene adhesive polyethylene adhesive                                                  polyethylene                        interm. layer  adhesive polyethylene EVOH PBT PET-G                           total thick'ss  0.5 mm 0.5 mm 0.5 mm 0.5 mm                                   diameter   25 mm  25 mm  25 mm  25 mm                                         internal heater                                                               air temp.  375° C. 375° C. 375° C. 375° C.                                                   air flow rate  410 (Nl/min)                                                  410 (Nl/min) 410 (Nl/min) 410                                                 (Nl/min)                            air suc. power  300 (Nl/min) 300 (Nl/min) 300 (Nl/min) 300 (Nl/min)                                                      water flow rate   2.2                                                        (l/min)  2.2 (l/min)  2.2                                                     (l/min)  2.2 (l/min)                heating time   1 (sec)  2 (sec)  0.8 (sec)  1 (sec)                           external heater                                                               air temp.  400° C. 400° C. 400° C. 400° C.                                                   air flow rate  380 (Nl/min)                                                  380 (Nl/min) 380 (Nl/min) 380                                                 (Nl/min)                            air suc. power  400 (Nl/min) 400 (Nl/min) 400 (Nl/min) 400 (Nl/min)                                                      water flow rate   4 (sec)  6                                                 (sec)  6 (sec)  6 (sec)                                                        heating time   22 (mm)  22                                                   (mm)  22 (mm)  22 (mm)                                                         (from front end)                 __________________________________________________________________________

Now, the second embodiment of the invention will be described. Thissecond embodiment relates to a tubular container 15 comprising athree-layer structure. In this second embodiment, the thickness and theproperties of each layer are discussed. The producing method and theproducing apparatus for this second embodiment are same as thosedescribed above and hence will not be described any further.

The inventor of the present invention conducted a series of experimentson tubular containers by using various resin materials having differentfluidity levels and by changing the thickness of each of the layers. Theinventor found that the thickness and the fluidity greatly affect therate of producing defective tubular containers. This will be describedby referring to Tables 2 and 3 summarizing the results of theexperiments. Note that the experiments were on the three-layer structurewhere the outer layer 61 and the inner layer 63 are made of sameadhesive polyethylene and the intermediary layer 65 is made of EVOH.

[Table 2]

In Table 2, the fluidity is expressed in terms of melt index(hereinafter referred to as MI). The MI was a value obtained byextruding a molten thermoplastic resin material with a predeterminedtemperature and pressure through an orifice having a predetermineddiameter and a length, weighing the extruded material, and reducing itinto the number of grains per 10 minutes. The method was conducted inaccordance with ASTM-D-1238. Generally, the higher the MI, the betterthe fluidity and workability. However, generally, the higher the MI, theless a tensile strength and a stress cracking resistance are worse.

In Table 2, the evaluation of the rate of producing good productsindicates as follows.

    ______________________________________                                        ⊚:                                                                      very low rate of producing defective products                          ◯: low rate of producing defective products                       ▴: relatively high rate of producing defective products                X: very high rate of producing defective products                   ______________________________________                                    

The term "defective product" as used herein refers to a product showingan abnormal projection on the shoulder section, a defectively thread, nooutlet or a similar defect.

In Table 2, the number of specimens of each experiment was 50.

                  TABLE 2                                                         ______________________________________                                               wall thickness d(μm)                                                                     MI                                                       experiment                                                                             outer  interm.  inner outer inner                                      No. layer layer layer layer layer rating                                    ______________________________________                                        1        225    50       225   1.6   1.6   ▴                     2 225 50 225 1.5 1.5 ▴                                         3 225 50 225 1.2 1.2 X                                                        4 300 50 150 1.6 1.6 X                                                        5 150 50 300 1.6 1.6 ◯                                            6 235 30 235 1.6 1.6 ▴                                       ______________________________________                                    

From Experiments Nos. 1 through 3 in Table 2, it is seen that if thethickness d3 of the outer layer 61 and the thickness d1 of the innerlayer 63 are made equal to each other and the outer layer 61 and theinner layer 63 are made of materials having a same level of fluidity,the produced tubular containers show a high rate of producing defectiveproducts

From Experiments Nos. 4 and 5 in Table 2, it will be seen that if thethickness d1 of the inner layer 63 is greater than the thickness d3 ofthe outer layer 61, the rate of producing good products is increased.

[Table 3]

Based on the result of the experiments indicated in Table 2, furtherexperiments were conducted. Table 3 summarizes the results obtained bymodifying the values for the thickness d2 of the intermediary layer 63and MI, provided that the thickness d1 of the inner layer 63 was greaterthan the thickness d3 of the outer layer 61.

In Table 3, the term "weld mark" refers to the linear flaw appearing onthe junction portion of thermoplastic resin. Generally, when two or moreflows of thermoplastic resin are poured into a metal mold to produce amold product and they are perfectly fused or mingled with each other, alinear flaw appears on the junction portion so as to degrade thecommercial value the product. Even if the linear flaw is not remarkablein appearance, the strength of the product perpendicular to the weldmark is significantly reduced if compared with a product having no weldmark and hence the product is more liable to give rise tostress-triggered corrosive cracking.

In Table 3, the evaluation of the weld mark indicates as follows.

    ______________________________________                                        ◯:                                                                             no remarkable linear flaw                                          ▴: somewhat remarkable linear flaw                             X: remarkable linear flaw                                                   ______________________________________                                    

The evaluation of the rate of producing good products is same as that inTable 2. In Table 3, the number of specimens of each experiment was 100.

                  TABLE 3                                                         ______________________________________                                        wall thickness d (μm)                                                                         MI                weld                                     experiment                                                                            outer  interm. inner outer                                                                              inner      mark                               No. layer layer layer layer layer rating rating                             ______________________________________                                        1       210    10      280   1.6  1.6   ⊚                                                                   X                                  2 200 30 270 1.6 1.6 ⊚ ◯                           3 210 10 280 1.5 1.5 ⊚ ◯                           4 200 30 270 1.5 1.5 ⊚ ▴                        5 200 50 250 1.5 1.5 ◯ X                                          6 210 10 280 1.5 1.6 ⊚ ◯                           7 200 30 270 1.5 1.6 ⊚ ◯                           8 200 50 250 1.5 1.6 ⊚ X                                     ______________________________________                                    

From the results of Experiments No. 1 and 6 of Table 3, it is seen thatthe high rate of producing good products can be realized or obtained bymaking the thickness d1 of the inner layer 63 greater than the thicknessd3 of the outer layer 61, and that the tubular container 1 in which theweld mark is not remarkable in appearance can be obtained by selecting agreater value of MI of the resin material of the inner layer 63 than avalue of MI of the resin material of the outer layer 61.

The results of Experiments Nos. 3-5 or Nos. 6-8 of Table 3 show thattubular containers 1 showing a remarkable weld mark are increased whenthe thickness d2 of the intermediary layer 65 is large.

In only the Experiments Nos. 5 and 8. the defect that the outlet 11 wasnot formed on the neck section 5 (hereinafter referred to as closedoutlet) was found. From this fact and the results of Experiments Nos.3-5 and Nos. 6-8, it is seen that a closed outlet is liable to occurwhen the thickness d2 of the intermediary layer 65 is large.

In view of the above description, when a three-layer thinly walled tube15 is used, it is preferable to meet the following requirements.

(1) The thickness d1 of the inner layer 63 is greater than the thicknessd3 of the outer layer 61.

(2) MI of the inner layer 63 is greater than that of the outer layer 61.

According to the third aspect of the invention, the tubular container 1can be provided with a marble pattern on the shoulder section. Accordingto the present invention, the marble pattern as shown in FIGS. 14 and 15may be applied when the shoulder section and the neck section are formedon the tubular container 1.

For producing a marble pattern on the shoulder section of the tubularcontainer 1, the thinly walled multilayer tube 15 is used and the layersof the tube are respectively colored with desired colors. For example,for producing a pink marble pattern on a white container, the outerlayer is colored to white, whereas the intermediary layer and/or theinner layer are colored to pink. Any appropriate known coloring agentsmay be used for coloring. The thinly walled tube shows an elliptic crosssection.

The above described producing method and producing apparatus can be usedfor producing the tubular container 1 carrying the marble pattern on theshoulder section and on the neck section. Therefore, the description ofthe first and second producing steps will be omitted here.

Referring to the third step of the method of producing the abovedescribed tubular container 1, the outer wall surface 21 of the thinlywalled tube 15 is heated by the heater 49, the hot air contacts with orhits to the outer wall surface 21, and the hot air is drawn and removedthrough the hot air suction path 51. Since hot air is made to hit theouter wall surface 21 and then drawn and removed in this way, thesoftened front end 15a of the thinly walled tube 15 shrinks or deformsinwardly, because of the positive pressure produced by the hot airhitting the outer wall surface 21 and the negative pressure produced bydrawing and removing hot air. As described above, the thinly walled tube15 has the elliptic cross section. Therefore, the contraction along thelonger axis is greater than the contraction along the short axis.Consequently, the front end 15b shows an indefinable profile as shown inFIG. 16 as if it is folded radially.

The fourth step is then conducted under this condition. As describedabove, the male mold 16 is lowered relative to the tube holder 17, andthe front end 15b of the thinly walled tube 15 is pinched between themale mold 16 and the female mold 27, which cooperate to form a necksection 5 and a tapered shoulder section 9 by compression molding. Sincethe folded portion is compressed and molded under this condition, thefolded portion shows phase difference, overlapping and displacementbetween the inner and outer layers. Thus, in the outer layer, astretched and thus thin portion is produced extending from the necksection to the periphery of the shoulder section. In this portion wherethe outer layer is made thin, the intermediary layer or the inner layercan be seen in appearance. Thus, at the shoulder portion, the color ofthe intermediary layer can be seen in appearance along the generatrix soas to produce a marble pattern along the generatrix.

EXAMPLE 6

In this example, a thinly walled tube 15 having a three-layer structurewas used. The outer layer and the inner layer were made of adhesivepolyethylene and the intermediary layer was made of EVOH. The outerlayer was colored to white. The inner layer was colored to pink. Theintermediary layer was not colored. The total wall thickness of thethinly walled tube 15 was 0.5 mm. The thinly walled tube 15 had a longerdiameter of 30 mm and a shorter diameter of 20 mm.

The internal heater 23 was used to produce hot air with temperature of375° C. and a flow rate of 410 N1/min. A hot air drawing power of 300N1/min was realized and a cooling water flow 2.2 1/min was used in thecooling section.

The external heater 25 was used to produce hot air with temperature of400° C. and a flow rate of 380, N1/min. A hot air drawing power of 400N1/min was realized and the heating was conducted for 4 seconds. Theheating range covered a length of 22 mm from the front end of the thinlywalled tube 15.

As a result, a good tubular container 1 was produced with a marblepattern on the neck section and the shoulder section.

As described above in detail, according to the invention, since the hotair used to heat the inner wall surface of the thinly walled tube isforcibly drawn and removed, no undesired area of the inner wall surfaceis heated and, since the outer wall surface of the thinly walled tube iscooled simultaneously and any possible deformation due to expansion isprevented, the profile of the thinly walled tube can be kept unchangedbefore and after the heating.

Additionally, since the hot air used to heat the outer wall surface ofthe thinly walled tube is forcibly drawn and removed, no undesired areaof the outer wall surface is heated. Thus, the volume of the portion tobe softened to produce the neck section can be held to a given level andthe shoulder section can be made to have a desired thickness so thatconsequently a tubular container having a desired profile can beobtained.

According to the invention, since a tubular container is formed directlyform a thinly walled tube, the tubular container is free from anyparting line. Therefore, the surface of a tubular container according tothe invention is highly adapted to printing. Still additionally, since atubular container can be manufactured without causing changes in theprofile of the heated thinly walled tube, so that the thinly walled tubemay be subjected to a printing operation in advance and only a necksection and a shoulder section may be formed out of it in the subsequentprocessing steps.

If the thinly walled tube is made to have a three-layer structure havingan intermediary layer sandwiched between the outer and inner layers, aflawless tubular container can be easily produced by making the innerlayer thicker than the outer layer or selecting a material having agreater level of fluidity for the inner layer than the material of theouter layer.

According to the invention, the shoulder section of a tubular containercan be made to bear a marble pattern when producing the tubularcontainer.

What is claimed is:
 1. A method of producing a tubular container havinga neck section for receiving a cap from a thinly walled tube ofthermoplastic resin, comprising:the first step of arranging the thinlywalled tube on a tube holder having a male mold for forming the necksection, a front end of the thinly walled tube projecting by a givendistance from a front end of the tube holder; the second step ofsoftening an inside of the front end of the thinly walled tube whilemaintaining a profile of the front end of the thinly walled tube bydischarging hot air onto an inner wall surface of the front end of thethinly walled tube, forcibly drawing the discharged air in a directionmoving away from said male mold, while an outer wall surface of thefront end of the thinly walled tube is cooled as a cooling surface isheld in contact with the outer wall surface, to establish a temperaturedifference between the inside and the outside of the thinly walled tube;the third step of shrinking the front end of the thinly walled tube bydischarging hot air onto the outer wall surface of the front end of thethinly walled tube, and forcibly drawing the discharged air in thedirection moving away from the male mold; and the fourth step of formingthe neck section and a shoulder section from the front end of the shrunkthinly walled tube by means of a female mold cooperating with the malemold.
 2. The method of producing a tubular container according to claim1, whereinan outlet for pouring out a content is produced in the necksection at the time when the neck section and the shoulder section areformed by compression molding.
 3. The method of producing a tubularcontainer according to claim 1, whereinthe thinly walled tube is amultilayer tube having at least two wall layers.
 4. The method ofproducing a tubular container according to claim 1, whereinthe thinlywalled tube is a three-layer tube having an intermediary layersandwiched by an outer layer and an inner layer, the intermediary layeris made of a material different from those of the outer and innerlayers, and the inner layer has a thickness greater than that of theouter layer.
 5. The method of producing a tubular container according toclaim 1, whereinthe thinly walled tube is a three-layer tube having anintermediary layer sandwiched by an outer layer and an inner layer, theintermediary layer is made of a material different from those of theouter and inner layers, and the material of said inner layer has afluidity greater than that of the material of said outer layer.
 6. Themethod of producing a tubular container according to claim 1, whereinthethinly walled tube is a three-layer tube having an intermediary layersandwiched by an outer layer and an inner layer, the intermediary layeris made of a material different from those of the outer and innerlayers, the inner layer has a thickness greater than the outer layer,and the material of said inner layer has a fluidity greater than that ofthe material of said outer layer.
 7. An apparatus for producing atubular container having a neck section for receiving a cap from athinly walled tube of thermoplastic resin, comprising:a tube holder thatholds the thinly walled tube, said tube holder including a male mold forcompression molding to be inserted into the thinly walled tube, saidmale mold being arranged inwardly in an axial direction from the frontend of the thinly walled tube by a given distance, said male mold beingaxially movable; an internal heater including a heating section thatdischarges hot air onto an inner wall surface of the front end of saidthinly walled tube, a cooling section outside the heating section withan annular gap provided therebetween, said cooling section having acooling surface that contact an outer wall surface of the front end ofthe thinly walled tube to cool the outer wall surface, and a hot airsuction path along which the hot air is drawn axially along the annulargap and away from the thinly walled tube after the hot air heats theinner wall surface; an external heater that discharges hot air onto theouter wall surface of the front end of said thinly walled tube, and theexternal heater including a hot air suction path that draws the hot airaxially in the direction moving away from the thinly walled tube afterthe hot air heats the inner wall surface; and a female mold that formsthe neck section and the shoulder section, said female mold cooperatingwith the male mold of said tube holder to pinch the front end of thethinly walled tube to form the neck section and the shoulder section bycompression molding.
 8. The apparatus for producing a tubular containeraccording to claim 7, whereinit is further provided with a piercingdevice for forming an outlet in the neck section when producing the necksection and the shoulder section by means of the male mold of the tubeholder and the female mold.
 9. The apparatus for producing a tubularcontainer according to claim 7, whereinthe front end of the thinlywalled tube held by the tube holder can be inserted into the annular gapbetween the cooling section and the heating section, and said heatingsection is provided with a loot air path therein and a hot air dischargeport at a position facing the cooling section with the thinly walledtube disposed therebetween.
 10. The apparatus for producing a tubularcontainer according to claim 7, whereinthe external heater includes anannular heating section provided with a hot air path therein, the frontend of the thinly walled tube held by the tube holder can be insertedinto the inside of the heating section, a suction path is connected tothe inside of the heating section, and said heating section is providedwith a hot air discharge port on the inner wall surface facing the frontend of the inserted thinly walled tube.
 11. A method of producing atubular container having a neck section for receiving a cap from athinly walled tube having at least inner and outer layers of differentcolors, the tube being made of thermoplastic resin and having anelliptic cross section including a long axis and a short axis, to form amarble pattern on the tubular container, comprising:the first step ofarranging the thinly walled tube on a tube holder having a male mold forforming the neck section, a front end of the thinly walled tubeprojecting by a given distance from a front end of the tube holder; thesecond step of softening an inside of the front end of the thinly walledtube while maintaining a profile of the front end of the thinly walledtube, by discharging hot air onto an inner wall surface of the front endof the thinly walled tube, forcibly drawing the discharged air in adirection moving away from said male mold, while cooling an outer wallsurface of the front end of the thinly walled tube, to establish atemperature difference between the inside and the outside of the thinlywalled tube; the third step of shrinking the front end of the thinlywalled tube by discharging hot air onto the outer wall surface of thefront end of the thinly walled tube to stretch the outer layer tothereby produce a thin portion in the outer layer wherein contractionalong the long axis is greater than contraction along the long axis isgreater than contraction along the short axis, and forcibly drawing thedischarged air in the direction moving away from the male mold; and thefourth step of forming the neck section and a shoulder section from thefront end of the shrunk thinly walled tube by means of a female moldcooperating with the male mold so that the inner layer can be seenthrough the thin portion of the outer layer, thus forming the marbledpattern.
 12. An apparatus for producing a tubular container having aneck section for receiving a cap from a thinly walled tube ofthermoplastic resin, comprising:a tube holder that holds the thinlywalled tube, said tube holder including a male mold for compressionmolding to be inserted into the thinly walled tube, said male mold beingarranged inwardly in an axial direction from the front end of the thinlywalled tube by a given distance, said male mold being axially movable;an internal heater that discharges hot air onto an inner wall surface ofthe front end of said thinly walled tube; an external heater thatdischarges hot air onto the outer wall surface of the front end of saidthinly walled tube; and a female mold that forms the neck section andthe shoulder section, said female mold cooperating with the male mold ofsaid tube holder to pinch the front end of the thinly walled tube toform the neck section and the shoulder section by compression molding,wherein the internal heater includes an annular cooling section forcooling the outer wall surface of the front end of the thinly walledtube, a heating section arranged inside the cooling section with anannular gap provided therebetween, and a hot air suction pathcommunicating with the annular gap between the cooling section and theheating section, the front end of the thinly walled tube held by thetube holder can be inserted into the annular gap between the coolingsection and the heating section, and said heating section is providedwith a hot air path therein and a hot air discharge port at a positionfacing the cooling section with the thinly walled tube disposedtherebetween.
 13. An apparatus for producing a tubular container havinga neck section for receiving a cap from a thinly walled tube ofthermoplastic resin, comprising:a tube holder that holds the thinlywalled tube, said tube holder including a male mold for compressionmolding to be inserted into the thinly walled tube, said male mold beingarranged inwardly in an axial direction from the front end of the thinlywalled tube by a given distance, said male mold being axially movable;an internal heater that discharges hot air onto an inner wall surface ofthe front end of said thinly walled tube; an external heater thatdischarges hot air onto the outer wall surface of the front end of saidthinly walled tube; and a female mold that forms the neck section andthe shoulder section, said female mold cooperating with the male mold ofsaid tube holder to pinch the front end of the thinly walled tube toform the neck section and the shoulder section by compression molding,wherein the external heater includes an annular heating section providedwith a hot air path therein, the front end of the thinly walled tubeheld by the tube holder can be inserted into the inside of the heatingsection, a suction path is connected to the inside of the heatingsection, and said heating section is provided with a hot air dischargeport on the inner wall surface facing the front end of the insertedthinly walled tube.